InAlN Barrier Layer for Normally-Off HEMT Substrate
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Solution Overview
Problem
Current nitride HEMT devices face challenges in achieving high two-dimensional electron gas concentration and normally-off operation due to limitations in epitaxial growth control, particularly with InAlN/GaN heterostructures, where the difference in growth temperatures complicates the formation of high-concentration 2DEG and reliable barrier layers.
Innovation Solution
A multi-layer epitaxial substrate structure is developed with a channel layer of Inx1Al1-x-y-zN and a barrier layer of Inx2Al2-y2-z2N, where the compositions are optimized within specific ranges to ensure high 2DEG concentration and normally-off operation, and a spacer layer with larger bandgap energy is introduced to enhance mobility and reduce drain leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the AlGaN barrier layer thickness is reduced to achieve normally-off operation, then the threshold voltage shifts to positive values, but the two-dimensional electron gas concentration becomes insufficient (5×10^12/cm^2 or less)
Solution Approach 1:
The invention changes the compositional parameters of the barrier layer by introducing InAlN with specific In content (0.15≤x≤0.25) to adjust the polarization effect and achieve normally-off operation while maintaining sufficient 2DEG concentration. It also changes the thickness parameter to an optimized range (3-7nm) that balances threshold voltage control with electron gas generation.
Solution Approach 2:
The invention uses a composite barrier layer structure combining AlN and InAlN materials. The AlN layer provides the necessary polarization effect for normally-off operation, while the InAlN layer with specific composition enhances the 2DEG concentration, achieving both requirements simultaneously.
2Quantity of substance
If InAlN/GaN heterostructure is used to achieve high 2DEG concentration by spontaneous polarization, then the piezo polarization effect is reduced, but the growth temperature control becomes difficult due to large difference between InN and AlN
Solution Approach 1:
The invention optimizes the In content parameter (0.15≤x≤0.25) to balance the polarization effect with growth controllability. This compositional parameter control allows achieving high 2DEG concentration while keeping the epitaxial growth process manageable despite the inherent temperature difference between InN and AlN.
Solution Approach 2:
The invention introduces a thin InAlN layer (3-7nm) with specific composition at the critical interface region between channel and barrier layers. This localized compositional adjustment enhances 2DEG concentration at the interface without requiring bulk material changes that would complicate the overall growth process.
3Quantity of substance
If the barrier layer thickness is increased to secure high 2DEG concentration, then the on-resistance increases, but if decreased to reduce on-resistance, then the 2DEG concentration becomes insufficient
Solution Approach 1:
The invention changes the material composition parameter by incorporating InAlN with specific In content (0.15≤x≤0.25) in the barrier layer. This compositional modification enhances the polarization effect per unit thickness, allowing achievement of high 2DEG concentration in a thin layer (3-7nm) that simultaneously maintains low on-resistance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The optimized substrate achieves a two-dimensional electron gas concentration of 1×10^13/cm^2 or more, enabling high mobility and low drain leakage current, while allowing for normally-off operation and improved breakdown voltage.
Implementation Method 1
high-concentration two-dimensional electron gas (2DEG) is generated at a lamination interface (hetero interface) owing to a large polarization effect (spontaneous polarization effect and piezo polarization effect) inherent in a nitride material
Data Source
AI summary
Provided is an epitaxial substrate capable of manufacturing a HEMT device that has excellent two-dimensional electron gas characteristics and is capable of performing normally-off operation. A channel layer is formed of a first group III nitride represented by Inx1Aly1Gaz1N (x1+y1+z1=1) so as to have a composition in a range determined by x1=0 and 0≦y1≦0.3. A barrier layer is formed of a second group III nitride represented by Inx2Aly2Gaz2N (x2+y2+z2=1) so as to have a composition, in a ternary phase diagram with InN, AlN and GaN being vertices, in a range surrounded by four straight lines determined in accordance with the composition (AlN molar fraction) of the first group III nitride and to have a thickness of 5 nm or less.